Question

A magnetic needle is fixed to a cork, which is floating in a still lake, on the Northern Hemisphere. The masses of the cork and the needle are very small. How will the needle move?

• A. The cork will move towards the northern corner of the lake
• B. The cork will move towards the southern corner of the lake
• C. The needle will not change position, but will rotate and align itself in North-South direction
• D. The needle will neither move nor rotate

Answer 1

The correct option is C The needle will not change position, but will rotate and align itself in North-South direction

A magnetic needle is nothing but a magnetic dipole which is placed in Earth's magnetic field.

Around the needle the Earth's magnetic field is uniform so that the needle will not experience any net force but will experience a torque.

It will align the needle in the direction of Earth's magnetic field, and it will remain in that position.

Hence, option $\left(C\right)$ is correct.